Metamorphism. The idea behind metamorphism is to alter the content of the virus itself, rather than hiding the content with encryption. The virus can be altered in several ways — for example, by adding unneeded code sequences to the source code or changing the sequence of pieces of the source code. The altered code is then recompiled to create a virusexecutable that looks fundamentally different from the original.

Anti-virus softwarevendors design their products to attempt to compensate for the use of any combination of obfuscation techniques. Older obfuscation techniques, including self-encryption, polymorphism, and stealth, are generally handled effectively by anti-virus software. However, newer, more complex obfuscation techniques, such as metamorphism, are still emerging and can be considerably more difficult for anti-virus software to overcome.